Different types of targets are used in target practice. The majority of targets used are penetrated by the shot round, to allow for an indication of the shooter's accuracy. Thermal targets, heated for detection with infrared sighting equipment are known for use in night training. Numerous heated targets are known in the art.
Long range firearm training generally requires specialized targets. Due to the large distance to the target, recovery of the target after a selected number of shots to judge the shooter's accuracy is impractical. Therefore long range targets are normally constructed for re-use. However, due to the high velocity of long range firearm ammunition, long range targets must be constructed of highly robust materials to allow re-use. Therefore, metal targets are used instead of the paper targets normally used in short range training. Moreover, long range metal targets must not only withstand repeated hits, but, more importantly, must be reactive, which means they must provide acoustic feedback to the marksman when hit, since visual observation of the shooter's accuracy is difficult.
Military groups employ long range metal targets made from sheets of R5400 steel or Hardox, generally approximately 1 cm thick. The targets are suspended from A-frames and are used as at-a-distance targets. In long range training, military marksmen are typically at such a distance from the target that visual verification of a hit is difficult and close range inspection of the target too time consuming. In such situations it is vital that the target be of the reactive type, producing an audible signal or acoustic feedback, when hit by a round.
As military technology has progressed, systems have been developed which allow marksmen to aim at a target during the night. They include night vision systems and thermal imaging systems. Night vision systems use image enhancement technology that makes use of lenses to collect small amounts of light, including from the near infrared spectrum, and to amplify and concentrate the light so that it becomes visible to the human eye. This acts to enhance the intensity range of a viewer's vision. When using night vision systems, targets such as R5400 steel blanks are visible due to their difference in reflectivity compared to the background.
Thermal imaging systems on the other hand make use of the fact that warm-blooded creatures have heat signatures (IR signatures) that differentiate them from the heat signature of the background. Thermal imaging systems are sufficiently refined, and sufficiently robust, to be used for in-field training. Target training with thermal imaging systems is however difficult, since targets, especially metal targets, do not generate a heat signature and generally take on the same temperature as their surroundings. Thus, they cannot be easily differentiated from the background. This is especially the case at long range firing distances. To better understand the problem, a brief understanding of thermal imaging is required.
Thermal imaging systems detect heat differentials between objects based on true infrared portions of the spectrum (900-1400 nm) as opposed to the near infrared portion of the spectrum. All bodies radiate energy in accordance with their temperature according to black body radiation laws. Thus objects having different temperatures can be differentiated from each other by the different thermal signatures that they provide. An IR sensing system can be employed to detect differential heat signatures and then provide a color-mapped image to a viewer.
A metal target of the type used in long range training will have a heat signature that is substantially similar to the signature of the background. This makes the standard metal target virtually indistinguishable by thermal imaging techniques. To address this problem, a number of techniques have been employed to imbue metal targets with a heat signature that can differentiate them from the background.
One technique makes use of chemical heating packs normally used by soldiers to heat meals. These chemical packs are placed on the metal target and then activated. The target is heated by a chemical reaction in the packs, and is then hung on the A-frame. The marksmen then proceed to the desired distance and attempt to fire at the target. This solution is far from ideal. Each of the packs can produce only a fixed amount of heat, and the high heat capacity of the target requires the use of a large number of heating packs. Furthermore, the specific heat capacity and high heat conductance of the metal target results in a heating and cooling curve that is not suited for long range training, since the time it takes for the shooter to set up the target and then proceed to the firing location significantly reduces the available training time.
Other attempts at heating the target have been made by hanging the target from the A-frame and then applying a stronger heat source, such as a blowtorch, to the target. This heats the target to a higher temperature and allows a longer lasting heat signature. However, the high heat from the torch can accelerate metal fatigue and significantly weaken the metal, thereby increasing the damage to the target upon impact and decreasing the lifespan of the target.
It is therefore desirable to provide a durable target that can be provided with a heat signature to allow for use with training of thermal targeting systems. U.S. Pat. No. 4,240,212 discloses a technique for simulating the thermal appearance of objects. Electrical energy is applied to a conductive material that is mechanically attached (staples, nails, screws) to a mounting surface shaped in the form of the selected target object. The conductive material is placed to simulate the radiation pattern that the object has been shown to demonstrate. The target object is not a reusable target and is penetrated by the fired ammunition. The target is also not a reactive target and the attachment of the heating structure would not withstand the repeated severe vibration which occurs in reactive targets.
U.S. Pat. No. 4,253,670 discloses thermal targets for use in night vision target training including a frame constructed of plywood having internal cavities forming a flue draft feeding to outside vents and a heat generating structure positioned in the bottom of the frame. Clearly, this target is neither reactive nor reusable, since penetrated by fired rounds and unable to withstand repeated severe vibration.
U.S. Pat. No. 4,260,160 discloses a target for night-time gunnery including a thin, supple fabric supported on a rigid frame with a front protective sheet, which is transparent to infra-red radiation and a rear radiation-absorbing sheet of low heat capacity. An infra-red radiator heats the heat-absorbing sheet which, when warmer than its surroundings, will radiate as a black body. This structure cannot be used as a reusable long range target.
U.S. Pat. No. 4,279,599 discloses an etched metal plate used to simulate an infrared target for trainees using sited weapons. Selectively etching the plate in a variety of fashions successfully imitates the thermal signature of the simulated target. The target is intended for use in simulated target exercises and is not for use with live rounds. Only simulated weapons are “fired” at the plate, which may be electrically heated by attaching a heater to a rear surface of the plate. Clearly, this target is not constructed for use with live ammunitions, nor is it constructed to withstand live round impact and the associated vibrations.
As is apparent, targets with localized heat sources are known, even those wherein the heat source is mounted onto the target by sandwiching it between layers of the target or by inserting it into a pocket on the target. However, none of the above discussed prior art teach any reusable long range firearm training targets. Moreover, attempts to attach secondary systems or structures to known long range reactive targets (acoustic targets) in the manner described in the art have been frustrated by the severe vibration stress to which such targets are subjected.
The percussive force of a long range firearm round is jarring and can dislodge or damage an associated structure used to heat the target. Due to the high velocity of long range rounds, the metal targets used are subjected to significant momentary deformation upon impact which generates severe vibrations in the target. These vibrations are so severe that they often lead to damage of bolted or welded connections on the target, for example for the connection to the target suspension structure. In long range targets, cracking and failure of bolts and welds are commonly observed after even a short period of use, due to this severe vibrations stress.
Long range targets, although constructed to withstand impact without penetration are often also permanently deformed, especially when used at the close end of the target range. Such permanent deformations place additional strain on the target already stressed by the repeated vibration load and accelerate target disintegration. Thus, using laminated structures and/or specialized pockets directly attached to the target for mounting a heating system to a long range percussive target are undesirable, since they will not be able to reliably withstand repeated use of the target.
Therefore, it is particularly desirable to provide a long range percussive target which is heatable and sufficiently durable to withstand the vibration stress during repeated use.